Microdensitometer scans were obtained and the laser bandwidth a t the absorption maxima was used as a measure of laser intensity. The quantitative results obtained are shown in Figure 11. The ratio of absorption to bandwidth falls off a t the higher concentration as total quenching of laser action commences. It is the opinion of the authors that continuous wave laser operation using nitrogen laser pumping in conjunction with photometric detection will be far superior to the preliminary approach described here for quantitative measurements. Atomic Quenching. Our observations of molecular quenching led naturally to a consideration of other absorbing species. The discovery that Peterson et al. (I), had observed sodium vapor quenching using heated glass cells prompted an investigation into the use of an atomic absorption flame within the resonant cavity of the laboratory constructed laser. During our ensuing investigation, it was noted that Ba+ and Sr have been detected as a transient species in an air-acetylene flame within a dye laser cavity (7). Initially, no problems were encountered in achieving normal laser output from rhodamine 6G with an air-acetylene flame in the cavity. Sodium-doublet absorption centered a t 589.2 nm was observed the first time a standard solution containing 60 ppm sodium was aspirated into the flame. Figure 12 shows the typical photographic data obtained in these experiments. Attempts to quantitate Na absorption have met with limited success. Absorptions from the laser band can consistently be seen for a wide range of concentrations if a number of parameters are optimized. These conditions include laser output, film speed, flame conditions, and band position. A linear concentration-absorption relationship has been seen over a narrow, low ppm range, but factors which we believe are inherent to the system itself have prevented definitive quantitation. The possibility of scatter by water droplets in the flame cannot be eliminated as a possible factor contributing to a variable laser output. Sodium absorption has been detected using solutions containing as little as
0.01 ppm sodium but the variability of the laser has prevented the establishment of any relationship between concentration and the extent of absorption. Solutions of mercury and barium salts have also been investigated. No problem has been encountered with barium since its resonance line lies within the range of fluorescein. In initial experiments, absorption has been detected using solutions containing 100 ppm barium. Rhodamine 6G has been used to detect mercury absorption a t 577 and 579 nm and the fluorescein compounds have been used for the 546 nm absorption line. Absorption has been noted for only a few of the many trials using 25-0.1 ppm mercury solutions. This is as expected because absorption a t these wavelengths is by excited state atoms, whose population is low in an air-acetylene flame. At the present time, the mercury resonance line a t 254 nm is beyond the range of available laser fluorescence.
(7) R. J. Thrash, H. von Weyssenhoff, and J. S. Shirk, J. Chem. Phys., 55.4659 (1971).
Received for review February 8, 1973. Accepted May 7 , 1973.
CONCLUSIONS The preliminary data reported here and by the other workers cited strongly indicate that intra-cavity quenching of laser fluorescence by absorbing species placed within the resonant cavity of a laser can be used to significantly enhance absorption measurements for the purpose of trace analysis. We feel this technique is a viable one, generally applicable to the determination of metals, permanent gases, and, very probably, organic vapors a t low concentrations. In the specific case of NOz, it could be immediately adapted for air pollution studies. The increased sensitivity, the limit of which has not been established, reduces the need for long path length absorption cells and/or sample concentration and conversion prior to measurement. At the present time, our studies are equipment limited, but we intuitively feel that continuous wave operation of the laser using nitrogen laser pumping and optical tuning will prove superior to the present pulsed mode. The ability to use photometric instead of photographic detection will certainly simplify quantitative studies.
Determination of Fluorine in Petroleum and Petroleum Process Catalysts with a Fluoride Electrode John Nevi1 Wilson and C. 2 . Marczewski The British Petroleum Company Limited, BP Research Centre, Chertsey Road, Sunbury-on-Thames, Middiesex. England
Fluoridation is known to enhance the activity of certain petroleum catalysts as shown, for example, by recent patents on the properties and use of fluorided hydrogenation catalysts (1-3). It may be required to determine fluorine levels in such catalysts during their period of use. Traces of organic fluorine can be produced in the processes, which may adversely affect subsequent operations. Fluo(1) C. Claude, E. E. Neel, and A . P. Anseime, U.K. Patent 1189930 (1970). (2) Robert J. White and Robert J. Houston, U.S. Paten1 3435085 (1969). (3) G. E. Elliot, Jr., J. Salomon, and R. F. Vogei, U.K. Patent 1277998 (1972).
rine must therefore be determined in process streams and products, sometimes a t sub-ppm levels. Environmental levels of fluorine are important because the element is an essential trace nutrient, but may cause the fluorosis of living matter if present in excessive concentrations. Data have been published of the fluorine levels in many materials, including soil ( 4 ) and coal ( 5 ) and a variety of foods. Until this present work, data have not been available for crude oils so far as we are aware, although figures for bromine and iodine have been pub(4) H A Shroeder, Arch E n v ~ r o nHeaith 21, 798 (1970) ( 5 ) F V Bethell J lnst Fuel 36,485 (1963)
ANALYTICAL CHEMISTRY, VOL. 45, NO. 14, DECEMBER 1973
2409
L7
8191855 ADAPTOR
i
lOml PIPET' WITH MODIFIED 1.5rnrn DIAMETER JET
FLOWMETER
0004
-
0002
-
1 I
I I
-I -I
-IF REAGENT BOTTLE
Figure 1 . Nitrogen chamber and reagent transfer system
lished (6). Possibly this lack of information arises from difficulties which have previously been associated with fluorine analysis (7) and which with the availability of the fluoride electrode, have been overcome. This paper describes procedures which have been developed for the preparation of analytical solutions from crude oils, residues, products, and process catalysts, suitable for the direct measurement of fluoride ion concentration with a fluoride electrode.
EXPERIMENTAL Apparatus. A Keithley Model 602 Solid State Electrometer was used to measure the potential difference between the Beckman Model 39600 fluoride electrode (8) and a conventional saturated calomel reference electrode. A special apparatus was made to permit the handling of sodium biphenyl reagent in an atmosphere of nitrogen (Figure 1). Reagents. Use analytical reagent grade chemicals, except where otherwise specified. Sodium Biphenyl Reagent. Prepare a solution in 1,e-dimethoxyethane (laboratory reagent grade, dried over 4A molecular sieve) as described by Pecherer and others (9). Transfer the freshly prepared reagent under dry nitrogen into 50-ml bottles with polythene-lined screw caps, seal tightly, and store in a refrigerator. Total Ionic Strength Adjustment Buffer. Use 1M sodium citrate, 0.5M potassium nitrate solution. Dissolve 294 g sodium citrate dihydrate and 50.5 g potassium nitrate in water to give a total volume of 950 ml. Adjust the pH to 6.0 with 2M citric acid, make up to 1liter with water, and store in a polythene bottle. (6) Gulf General Atomic Inc. for US Atomic Energy Commission, "De-
velopment of Nuclear Analytical Methods for Oil Slick Identification (Phase l ) , "San Diego. Calif.. 1970. (7) "Comprehensive Analytical Chemistry," C. L. Wilson and D. W . Wilson, E d , Vol IB. Elsevier, 1960 p 551 (8) Orion Research Association, U.K. Patent 1131574 (1968). (9) 6. Pecherer, C. M . Gambrill, and G . W. Wilcox, Anal. Chern.. 22, 311 (1950). 2410
ANALYTICAL CHEMISTRY, VOL. 45, NO. 14, DECEMBER 1973
Table I. Fluorine Content of Fluorided Catalysts Fluoride, % w / w Other active constituents
Matrix
W, Pod3-
Pt, Fe Pt Pt Pt Pt Pt Ni, Co, Mo Ni, Co, Mo
By fluoride
electrode
By thorium nitrate titration
6.68; 6.74 5.80; 5.78 4.80; 4.87 4.71; 4.78 4.58; 4.52 1.80; 1.74 6.6 ; 16.4 3.56 4.60; 4.59 2.40; 2.37 3.13; 3.14 6.64 3.15; 3.13
6.30; 6.55 5.84; 5.23 5.12; 4.71 4.92; 4.93 4.25; 4.47 1.87; 1.83 7.4 ; 18.2 3.49; 3.85 4.64; 4.98 2.55; 2.61 2.77; 2.91 6.03; 6.36 3.11; 2.75
Table I t . Fluorine in Crude Oils Crude oil
Alaskan Arabian light Arabian heavy Iranian light I ranian heavy Iraq (Basra) Iraq (Mediterranean) Kuwait Libyan Nigerian (Forcados)
Table 1 1 1 . Fluorine in Petroleum Products Product Fluorine, pprn wt
a
0.96; 0.20; 0.22; 0.19; 0.12; 0.35; 0.15; 0.15; 0.25; 0.18;
1.08 0.18 0.37 0.16 0.14 0.36 0.16 0.14 0.26 0.27
a
RESULTS AND DISCUSSION Fusion Flux. A borax-alkali carbonate fusion mixture was chosen because it is sufficiently vigorous to ensure decomposition and dissolution of highly refractory materials such as calcined alumina, and can therefore be applied to the majority of petroleum catalysts. Losses of fluorine as BF3 said to occur with fluxes containing borax (11) were not observed. This accords with the findings of Oli(11) J . A . Voinovitch, J . Debras-Guedon, and J . Louvrier, "The Analysis
of Silicates," Israel Program for Scientific Translations, Jerusalem,
0.06; 0.06 0.09; 0.08 0.17; 0.17; 0.20
